/**
 * Headless-Firefox screenshot helper (W3C WebDriver via geckodriver):
 *
 *   node dev/shot-firefox.mjs <url> <pollExpr> <outPng> [timeoutMs=25000]
 *
 * <pollExpr> is evaluated with execute/sync and polled until it returns
 * a non-null value (the page should set the state first), then the
 * session's screenshot is saved to <outPng>.
 */
import { spawn, execFileSync } from 'node:child_process';
import { existsSync, readdirSync, writeFileSync } from 'node:fs';

const [url, expr, outPng, timeoutMs = '30000'] = process.argv.slice(2);
if (!url || !expr || !outPng) {
  console.error('usage: node dev/shot-firefox.mjs <url> <pollExpr> <outPng> [timeoutMs]');
  process.exit(2);
}
const sleep = (ms) => new Promise((r) => setTimeout(r, ms));

let geckodriver;
try {
  geckodriver = execFileSync('sh', ['-c', 'command -v geckodriver'], { encoding: 'utf8' }).trim();
} catch {
  console.error('need firefox + geckodriver on PATH');
  process.exit(2);
}
const firefoxCandidates = [];
try {
  const ff = execFileSync('sh', ['-c', 'command -v firefox'], { encoding: 'utf8' }).trim();
  if (ff) firefoxCandidates.push(ff);
} catch { /* not on PATH */ }
try {
  const snapRev = readdirSync('/snap/firefox', { withFileTypes: true }).map((d) => d.name);
  for (const rev of [null, ...snapRev]) {
    const base = rev ? `/snap/firefox/${rev}` : '/snap/firefox/current';
    const p = `${base}/usr/lib/firefox/firefox`;
    if (existsSync(p)) firefoxCandidates.push(p);
  }
} catch { /* no /snap/firefox */ }
if (firefoxCandidates.length === 0) {
  console.error('no firefox binary found');
  process.exit(2);
}
const PORT = 4444 + (process.pid % 100);
const driver = spawn(geckodriver, ['--port', String(PORT), '--log', 'fatal'], { stdio: 'ignore' });
const base = `http://127.0.0.1:${PORT}`;

const fail = (msg) => {
  try { driver.kill('SIGKILL'); } catch { /* dead */ }
  console.error(msg);
  process.exit(1);
};

const wd = async (method, path, body) => {
  const res = await fetch(base + path, {
    method,
    headers: { 'Content-Type': 'application/json' },
    body: body === undefined ? undefined : JSON.stringify(body),
  });
  const text = await res.text();
  let data = null;
  try { data = JSON.parse(text); } catch { /* empty */ }
  if (!res.ok) throw new Error(`WebDriver ${method} ${path} → ${res.status}: ${text.slice(0, 300)}`);
  return data;
};

try {
  let up = false;
  for (let i = 0; i < 60; i++) {
    try {
      const v = await (await fetch(`${base}/status`)).json();
      if (v?.value?.ready || v?.status === 'ok' || v?.value) { up = true; break; }
    } catch { /* not up */ }
    await sleep(250);
  }
  if (!up) fail('geckodriver never came up');

  let sess;
  let lastErr = null;
  for (const ff of firefoxCandidates) {
    try {
      sess = await wd('POST', '/session', {
        capabilities: {
          alwaysMatch: {
            browserName: 'firefox',
            'moz:firefoxOptions': {
              args: ['-headless'],
              binary: ff,
            },
          },
        },
      });
      break;
    } catch (err) {
      lastErr = String(err?.message ?? err);
    }
  }
  if (!sess) fail(`no firefox candidate accepted: ${lastErr}`);
  const sid = sess.value?.sessionId;
  await wd('POST', `/session/${sid}/window/size`, { width: 1280, height: 720 }).catch(() => {});
  await wd('POST', `/session/${sid}/url`, { url });

  const deadline = Date.now() + Number(timeoutMs);
  let pollErr = null;
  while (Date.now() < deadline) {
    await sleep(300);
    try {
      const r = await wd('POST', `/session/${sid}/execute/sync`, { script: expr, args: [] });
      if (r.value !== undefined && r.value !== null) break;
    } catch (err) {
      pollErr = String(err?.message ?? err);
    }
  }
  await sleep(400); // let the last frame paint
  const shot = await wd('GET', `/session/${sid}/screenshot`);
  writeFileSync(outPng, Buffer.from(shot.value, 'base64'));
  console.log(`saved ${outPng}${pollErr ? ` (last poll error: ${pollErr})` : ''}`);
  await wd('DELETE', `/session/${sid}`).catch(() => {});
} finally {
  try { driver.kill('SIGKILL'); } catch { /* dead */ }
}